This document discusses the different levels of protein structure: primary, secondary, tertiary, and quaternary. The primary structure refers to the amino acid sequence in the polypeptide chain. Secondary structure involves localized folding patterns like alpha helices and beta sheets. Tertiary structure describes the overall 3D shape of the protein, which is determined by interactions between amino acid side chains. Quaternary structure refers to the arrangement of multiple polypeptide subunits in a single protein complex.

1. BY- MANIKANT MANI
M.Sc microbiology
sem- 1

2. INTORDUCTION
Protein structure is the three-dimensional
arrangement of atoms in an amino acid-chain
molecule. Proteins are polymers – specifically
polypeptides – formed from sequences of
amino acids, the monomers of the polymer. ...
Very large aggregates can be formed
from protein subunits.

3. Proteins are an important class of biological macromolecules which
are the polymers of amino acids.
 Biochemists have distinguished several levels of structural
organization of proteins. They are:
Primary structure
Secondary structure
Tertiary structure
Quaternary structure

4. PRIMARY STRUCTURE
The primary structure of protein refers to the sequence of amino
acids present in the polypeptide chain.
Amino acids are covalently linked by peptide
bonds.
Each component amino acid in a polypeptide is
called a “residue” or “moiety”
By convention, the 10 structure of a protein
starts from the amino-terminal (N) end and
ends in the carboxyl-terminal (C) end.

5. PRIMARY STRUCTURE

6. SECONDARY STRUCTURE
 Localized arrangement of adjacent amino
acids formed as the polypeptide chain folds.
 It consists of
α-helix
β-pleated sheet
β-bends
Non repetitive structures
Super secondary structures

7.  Linus Pauling proposed some essential features
of peptide units and polypeptide backbone.
They are:
– The amide group is rigid and planar as a
result of resonance. So rotation about C-N
bond is not feasible.
– Rotation can take place only about N- Cα
and Cα – C bonds.
– Trans configuration is more stable than cis
for R grps at Cα
 From these conclusions Pauling
postulated 2 ordered structures α helix
and β sheet.

8. SECONDARY STRUCTURE

9. TERTIARY STRUCTURE
 Tertiary structure is the three
dimensional conformation of a
polypeptide.
 The common features of protein
tertiary structure reveal much about
the biological functions of the proteins
and their evolutionary origins.
 The function of a protein depends
on its tertiary structure. If this is
disrupted, it loses its activity.

10. DOMAINS
Polypeptide chains containing more than ,200
residues usually fold into two or more globular clusters
known as domains.
Fundamental functional and 3 dimensional
structure of proteins.
Domains often have a specific function such as the
binding of a small molecule.
Many domains are structurally independent units
that have the characteristics of small globular proteins

11. DOMAINS
The two-domain protein glyceraldehyde- 3
phosphate dehydrogenase.
NAD+

12. INTERACTIONS STABILIZING 30 STRUCTURE
This final shape is determined by a variety of
bonding interactions between the "side chains“ on the
amino acids.
Hydrogen bonds
 Ionic Bonds
 Disulphide Bridges
 Hydrophobic
Interactions:

13. TERTIARY STRUCTURE

14. DETERMINATION OF TERTIARYSTRUCTURE
• The known protein structures have come to
light through:
• X-ray crystallographic studies
• Nuclear Magnetic Resonance studies
• The atomic coordinates of most of these
structures are deposited in a database known
as the Protein Data Bank (PDB).
• It allows the tertiary structures of a variety
of proteins to be analyzed and compared.

15. QUATERNARYSTRUCTURE
• The biological function of some molecules is
determined by multiple polypeptide chains –
multimeric proteins.
• Arrangement of polypeptide sub unit is called
quaternary structure.
• Sub units are held together by non covalent
interactions.
• Eg: Hemoglobin has the subunit composition
a2b2

16. Quaternary structure of
hemoglobin
Quaternary structure
of hemoglobin.

17. Thank you…
Manikant mani
email.-manikant8541@gmail.com